1. Field of the Invention
The present invention relates to a pattern of a bar tacking stitches.
2. Description and Problems of the Related Art
A lockstitch bar tacking sewing machine performs a cycle of sewing operation to form a given number of stitches for lockstitch sewing, button sewing, etc., and a bar tacking stitch pattern is formed using the lockstitch bar tacking sewing machine. Conventionally for buttonholing, bar tacking is applied to the starting and ending portions of overedge chain stitches using a sewing machine of this kind after the same are formed around a buttonhole. The bar tacking stitch pattern D is formed by performing 1.5 cycles of reciprocation of lateral sewing, i.e., forming three lateral stitches D1 as illustrated in FIG. 5, and thereafter forming zigzag stitches D2 from right to left over the lateral stitches D1, each segment of the zigzag stitches D2 extending almost vertically. In forming these lateral stitches D1, double or triple stitches 2, 4, etc. are formed about the central portion of the stitch pattern. In FIG. 5, denoted at 1 to 28 are stitches.
A conventional lockstitch bar tacking sewing machine applies such a bar tacking stitch pattern D to overedge chain stitches formed around a buttonhole C made by a cutter in the process of forming the overedge chain stitches during the holing operation, and creates a technical problem. Double or triple stitches 2, 4, etc. are formed adjacent to the center of the sewing pattern, i.e., where the sewn product 29 does not exist, in forming the lateral stitches D1 so that shrunk portions are formed in a sewn product 29 due to the tension of the sewing thread. Consequently the zigzag stitches D2 which is thereafter formed from right to left over the lateral stitches D1, becomes uneven due to the shrinkage of the sewn product 29 to make the stitch pattern irregular. Although the above problem of the irregular stitch pattern does not take place if the bar tacking stitch pattern D is formed sufficiently apart from the end portion of the buttonhole C in the extending direction thereof so as to prevent the stitch pattern D from being influenced by the slit of the buttonhole C, it is impossible to form a decent buttonholing stitch pattern including the bar tacking stitch pattern D at the end portion of the buttonhole C.
Although the slit of the buttonhole C is closed when the bar tacking stitch pattern D is formed by such a lockstitch bar tacking sewing machine, it does not settle the above technical problem. The closing operation of the slit of the buttonhole C is performed employing a work holder equipped with clamp feet and a feed plate for clamping the sewn product therebetween, wherein the right and left clamp feet which are positioned a little apart from each other press down the sewn product and thereafter are brought close to each other.